The Sikorsky–Boeing SB-1 Defiant is the jointly developed by Sikorsky Aircraft and Boeing for the United States Army's Future Vertical Lift program. It is a compound helicopter with rigid coaxial rotors, powered by two Honeywell T55s, and should make its first flight early in 2019. The Defiant is designed to fly at twice the speed and range of today’s conventional helicopters and offers advanced agility and manoeuvrability, according to the Sikorsky-Boeing team. The aircraft is intended to replace the Sikorsky UH-60 Black Hawk and the Boeing AH-64 Apache. Data from the Defiant will help the Army develop requirements for new utility helicopters expected to enter service in the early 2030’s.
Sikorsky–Boeing SB-1 Defiant
Sikorsky UH-60 Black Hawk Boeing AH-64 Apache
The Sikorsky-Boeing team says it needs to put at least 15h of testing time on the powertrain test bed before a flight safety committee will approve the SB-1's first flight. The two companies are now focusing on implementing fixes so the test bed can start running again within one or two weeks. Once flight testing begins, the aircraft will be evaluated by the Army for further development. Sikorsky is leading the development of phase one with an aircraft based on their previous Sikorsky X2 design.
The timeline for the first flight has slipped several times. Originally scheduled for 2017, delays arose due to a requirement to implement automated fibre placement blade manufacture at the request of the U.S. Army. Further delays resulted in the first flight slipping past mid-2018. Dynamic systems like turboshafts, transmission, and rotors were scheduled to be tested at West Palm Beach, Florida, by the end of October 2018, before ground runs in November, then first flight to reach 200 knots within six months. The first prototype was unveiled in December 2018, and the first flight was pushed to sometime in early 2019.
SB-1 Defiant Prototype
Boeing plans to lead phase two, which is the mission systems demonstrator phase. The Boeing-Sikorsky team is seen to have an advantage, given their big industrial base that should result in wider support from Congress, the fact that their transport helicopter designs are currently the most used in the Army, and because the US Army has had little interest in tilt-rotor technology, like that submitted by Bell.
The team feels confident in the SB-1 Defiant and is paying for more than half of its design costs. The last project the companies teamed up for was the RAH-66 Comanche, which started in the 1980s and cost $7 billion before being cancelled in 2004. They say that factors outside their control, like budget cuts, "requirement creep", and a long development period caused problems with the Comanche and not team dysfunctional. Under the Comanche program, each company built different parts of the aircraft.
Sikorsky–Boeing states the SB-1 will be quick and nimble, with fast acceleration and deceleration, side-to-side movement, and hovering with the tail up and nose down. The Defiant demonstrator will be powered by the Honeywell T55, which powers the CH-47 Chinook. It will be slightly modified to better operate at slower speeds down to 85% rpm.
The design will have a cruise speed of 250 kn, but less range due to using the "old" T55 engine. A new engine, the future affordable turbine engine (FATE), is to meet the range requirement of 229 nmi. Compared to conventional helicopters, the counter-rotating coaxial main rotors and pusher propeller offer a 100 kn speed increase, combat radius extended by 60%, and performs 50% better in high-hot hover performance.